The present invention relates to battery stack control systems.
Battery stacks include a plurality of individual “cells” are arranged in series in order to build a battery stack having a desired output voltage. A large number of cells may be arranged in series such that, for example, the total potential difference developed across the battery stack is in the order of a several hundred volts. Each cell typically only has a potential difference of a few volts (e.g., 3 volts) developed across it. Battery stacks also include a switch control, which can be used to switch cells individually in and out of the stack and control the orientation of the cells (e.g., positive or negative orientation) within the stack to meet timing requirements. Battery stacks can be used to generate time-varying outputs (e.g., sinusoidal signals) about a ground value (e.g., +300 volts to −300 volts in a 100 cell stack).
Rechargeable battery stacks can be used in many applications. One such application is the use of batteries in hybrid or fully electric vehicles. Hybrid and fully electric vehicles (HEV/EVs) are becoming increasingly popular, therefore there is a need for more effective, efficient, and safe battery stack systems. Conventional battery stacks suffer from several problems during operation. For example, because each of the cells in a battery stack discharges at a different rate, some cells may become too weak to supply voltage to a load. In such a case, the weakened cell can be permanently damaged if it is forced to discharge further and will eventually need to be replaced. Similar problems occur when a fully charged cell is over-charged. Additionally, if a cell is damaged beyond repair, the stack needs to continue to operate as required by the load. Conventional battery stacks fail to adequately account for such errors. Finally, when battery stacks are exposed to hazardous conditions (e.g., when they are submersed in water), they can become flammable, causing serious safety issues. This problem is specifically dangerous because there is a reasonable likelihood that consumers will be in close proximity to battery cells.
Thus, there is a need for improved battery stack monitoring systems to account for the problems described above.